1. Field of the Invention
This invention relates to a method of evaluating silicon wafers, particularly to a method adapted to evaluate the quality of mirror polishing of silicon wafers and the quality of the grinding process for silicon wafers, which is an important factor affecting the quality of silicon wafers.
2. Description of Prior Art
Silicon wafers employed in semiconductor devices are sliced from silicon single crystals, which are usually manufactured by the CZ or FZ method. The outer peripheries of the sliced silicon wafers are chamfered, then processes such as grinding, lapping, and polishing are performed on both of the front and rear surfaces so as to mirror-finish at least one surface.
Grinding and polishing semiconductor wafers to be mirror-finished produces process faults (hereinafter referred as defects) such as scratching capable of being detected by eyesight inspection and local residual strains undetectable by the naked eye. According to JP-A 8-70009 (JP-A: Japanese unexamined Patent Publication) entitled "METHOD OF MANUFACTURING SEMICONDUCTOR SILICON WAFERS", the existence of residual strains undetectable by the naked eye can be recognized by using a microscope if selective etching is performed on a silicon wafer. Furthermore, the above residual strains can be removed by applying heat treatment to silicon wafers within a short time period at low temperature.
The above method of manufacturing semiconductor silicon wafers is adaptable for removing residual strains induced during mirror polishing on surfaces of silicon wafers, the result can be recognized by performing selective etching. However, even if selective etching has been performed, it is impossible to predict the extent to which the recognized defects will adversely affect the important qualities of semiconductor devices, for example the electrical characteristic such as oxide film insulation. Therefore, it is difficult to isolate the quality-control problems in the processing of silicon wafers and improve them.